JPH0772693B2 - Coriolis type mass flow measuring device - Google Patents

Description

Detailed Description of the Invention

[0001] Generally speaking, the present invention relates to a Coriolis force type mass flow measuring device utilizing at least one flow tube fixedly mounted in a girder shape. More specifically, the above method is accurate, The present invention relates to an improvement in a device using the novel sensor and circuit configuration used in order to substantially increase stability and flexibility.

The present invention provides an improvement over previously known flow meter concepts and is described in US Pat. No. 41.
No. 87721, a Coriolis force type mass flow meter including a continuous flow tube attached to a girder is used to measure the mass flow rate of a flowing fluid, and a new sensor and circuit structure therefor are provided. To use.

The sensor used in the novel measuring device according to the present invention enables an accurate measurement of the Coriolis force by outputting an analog signal which accurately represents the overall vibrational movement of the flow tube.

In this respect, the sensor according to the invention outputs a digital signal with reference to the structure provided on the mounting platform of the flow meter and thus in dependence on the position of the central point where the vibration is fixed. It is different from previous sensors.

Digital signals in prior art sensors are essentially references to "static" structures and static midplanes with respect to an oscillating conduit over a time span of one cycle of oscillation. is there. Like this "static"
Avoiding the use of physical structures as a digital reference means includes changes in the structures and especially spatial orientation of the flow meter caused by fluctuations in external conditions such as temperature and fluid pressure. The manual compensation process required for variations in the physical properties of the conduit, such as the spatial orientation of the conduit, is eliminated.

According to the present invention, the above-mentioned difficulties can be solved. For this reason, the present invention provides: (a) at least one continuous conduit with both open ends fixed and adapted to be oscillated by being biased by the driving means, and (b) both ends fixed with the conduit substantially. Is a vibrating member arranged in parallel with
A vibrating member having substantially the same resonance frequency as the conduit and vibrating in opposite phase to the conduit so as to operate in a tuning fork shape, (c) a driving means for vibrating the conduit and the vibrating member, (d) A sensor means comprising at least a pair of substantially identical sensors for producing an electrical signal in response to movement of the conduit, each of the pair of sensors being (i) substantially equal from each end of the conduit. A sensor means disposed along the conduit at a distance and (ii) substantially equidistant from the central point of the conduit,
(E) the signal processing means, (f) the mass flow rate of the fluid flowing through the conduit at each and every time point at which the conduit portion adjacent to one of the pair of sensors passes a given point in its vibration path. , And each time point at which the portion of the conduit adjacent the other sensor of the pair of sensors passes through the point corresponding to the given point in its path of vibration, as a function of the time difference between Flow rate reading means,
And the sensor means comprises at least a pair of magnetic velocity sensors, each magnetic velocity sensor is composed of a magnet and a coil, and the coil always moves in a uniform magnetic field of the magnet corresponding to the coil. And a magnetic velocity sensor, each of which produces a continuous signal representative of the velocity of the portion of the conduit adjacent to the sensor throughout the oscillatory motion of the conduit and signal processing means. Is at least a pair of circuit portions formed of the same circuit element, each consisting of a circuit portion that is similarly connected to the output of one coil of the pair of magnetic speed sensors, and Each circuit part is configured to conduct the output from the sensor coil through at least one stage integrator, and to measure the mass flow rate of the fluid. Featuring at providing a re-mass flow measuring device.

Rather than utilizing a velocity sensor to determine the Coriolis force as a function of the magnitude of the velocity of the conduit, the present invention provides the velocity sensor with an accurate signal corresponding to the overall travel of the vibrating conduit. So that the delay time between the movements of two corresponding opposing portions, such as the two legs of the vibrating tube, caused by the Coriolis force induced by the mass flow through a given vibrating plane is determined. To use.

As will be made clear in the discussion below, techniques for analogically measuring the motion of a conduit as a function of velocity include a fixed central point or "static" discrete (for a dynamic or oscillating conduit). It does not seek a reference means for a discrete physical structure.

Therefore, this analog measurement is disclosed in Patent No. 4
When using a Coriolis force mass flowmeter such as that shown in FIG. 1 of 187721, it is independent of long-term structural directional fluctuations caused by changes in external conditions. Compensation for these external conditions requires the compensation of the position of the discrete and "static" structure. For velocity sensors, this independence from fluctuations is due to the fact that the strain caused by changes in the external conditions of the flowmeter structure is substantially smaller in magnitude than the specific reference means of the sensor. There is. In the measuring device of the present invention, the signal of each sensor is at least once,
It is preferably integrated a plurality of times, and each output of the integrator is returned to the input side of the integrator through a low-pass negative feedback circuit. The steps in this device minimized the sensitivity to external vibrations that induce harmonics in the sensor output signal and generated it in the integrator circuit independent of the phase of the sensor signal. The drift is eliminated and further low frequency components in the sensor output signal are removed, i.e. below the frequency of the conduit being driven.

Accordingly, it is an object of the present invention to provide a "static" reference means for a mechanical structure fixed to a fixed central point of a flow meter or to a mounting platform, rather than (1) dynamically. An accurate mass flow rate measurement method based on various reference means, and (2) an improved mass flow rate measurement device having the property of compensating structural fluctuations caused by changes in external conditions. It is to be.

Another object of the present invention is to provide an improved mass flow measuring device which is insensitive to vibrations transmitted through the structure of the flow meter which affect the sensor output signal.

It is another object of the present invention to provide an improved mass flow measurement device that is substantially insensitive to dynamic environments such as temperature and fluid pressure.

These and other objects and features of the present invention will be apparent from the following description and drawings.

Attention is now directed to the drawings, where like components are designated with like reference numerals throughout the various drawings.

An exemplary flow meter suitable for implementing the device of the present invention is depicted in FIG. 1 and is designated generally by the reference numeral 10.

This illustrative flow meter 10 is in many respects similar to that described in US Pat. No. 4,187,721. It should be readily understood that the measuring device of the present invention can be used for flowmeters of various shapes other than those described here without departing from the scope of the present invention.

Among the findings shown in the above patent, the following characteristics of the flowmeter 10 shown in FIG. 1 are particularly closely related to the present invention.

That is, the flow meter includes a platform 12 to which one conduit 14 is attached. The conduit 14 is attached by a tube support 26 proximate to the cantilevered inlet 15 and outlet 16 for rotational vibration without the use of pressure sensitive joints. The illustrated conduit 14 has lateral legs 18 and 20 with a transverse joint 2 extending therebetween.
It is provided with 2.

In the above example, a drive mechanism 25, usually in the form of a magnet and coil, is carried on the conduit 14 and the reciprocating oscillating member 30, and by means of a well known drive circuit 27 the conduit 1
4 oscillates about axis W--W, so that Coriolis deflection forces are driven to cause deflection of conduit 14 about axis O--O.

The reciprocating vibration member 30 may have various shapes. For example, it may be a single leaf spring, a V-shaped member with its wide end attached and fixed, or the rectangular structure shown.

The vibrating member 30 has a resonance frequency substantially the same as that of the conduit 14 when the conduit 14 is filled with fluid. The vibrating member and the conduit 14 are attached so that they both form a tuning fork during operation.

Therefore, the conduit 14 and the vibrating member 30 are driven by the drive mechanism 25 at a common resonance frequency.

In the measuring device according to the invention, the preferred sensors 33, 33 'each produce a linear continuous signal which accurately represents the overall vibration of the conduit 14. This point is different from the specific example in the above-mentioned US Pat. No. 4,187,721. In said patent, the deflection of the conduit digitally causes the passage of both legs of the oscillating conduit at a center point relative to the passage of a fixed mechanical structure with respect to the oscillating conduit located at a fixed center point of the path of vibration. It is measured by detecting.

In the prior art embodiment described above, sensors were placed on the side legs 18, 20 of the conduit 14,
By placing a fixed structure that cooperates with the sensor portion attached to the conduit to generate only a digital signal at the center of vibration, the generated timing signal of legs 18 and 20 passing through the center of vibration is It was used to determine the delay time between.

According to US Pat. No. 4,187,721, this delay time is multiplied by a constant dependent on the geometry of the conduit 14 to equal the mass flow rate through the conduit.

The measuring device according to the invention takes advantage of this latter finding, but by the unique method described here the delay time of the passage of the legs 18 and 20 through a given plane of the passageway of the vibration of the conduit is determined. By making use of this, it is possible to utilize the mass flow measurement with higher accuracy.

The significance of the output signals of the sensors 33, 33 'will be better understood with reference to FIG.

As shown in FIG. 2, the position of the conduit is plotted on the vertical axis and the time is plotted on the horizontal axis. Under ideal conditions, as is specifically contemplated in U.S. Pat. No. 4,187,721, a line A-C representing a "static" center point causes the fluid to flow around a fixed center plane under conditions of no fluid flow. Vibrations are identified.

However, under actual working conditions, including changes in temperature and pressure of the fluid flowing through conduit 14, vibrations of the mounting platform, etc., the vibration of conduit 14 is displaced relative to a fixed center point. To typically occur around a particular point in the transit path of the fluctuating vibration as depicted by the curve shown.

For example, if the temperature first deviates from a constant state and then rises, and then the temperature deviates and then deviates, it is actually the point at which a symmetric vibration occurs around a specific point in the path of the nominal static vibration. Only in A, B and C. Thus, the actual vibration, although exaggerated for graphical reasons, occurs symmetrically around the curve representing the changing center point.

Thus, FIG. 2 shows that the normally static center point of vibration deviates from the actually fluctuating center point under fluctuating external conditions.

To eliminate the need for recalibration in response to center point drift as a result of deviations of the vibration from the actual center point as shown in FIG. 2, the flowmeter shown in FIG. It utilizes a sensor that produces an analog signal that is a linear representation of all of the actual vibrations of this, unlike the one that produces a digital signal associated with a structure fixed to the mounting platform of this point flowmeter.

The speed sensor shown in FIG. 1 is located at the joint 22 remote from the axis WW. Sensor 33,3
3'is preferably located at the outer edge of legs 18, 20 as shown in FIG.
What is important is that the sensor is always placed symmetrically opposite the conduit.

For convenience of discussion, the velocity sensor depicted in FIGS. 3 and 4 is taken as an example, but it may be another sensor.

Referring to FIG. 3, the speed sensor 40 is
Included are two magnets, preferably permanent magnets 42, which are fixedly mounted to mounting platform 12 adjacent the conduit in an embodiment of the invention as shown in FIG. The sensor 40 also includes a bobbin 44 that carries a coil 45 and may be attached to the conduit.

Referring to FIG. 4, the coil winding is a magnet 4
The two magnetic pole faces 47 and 48 are located close to each other, and are always placed in a uniform magnetic flux field except for the straight line portion connecting the winding ends located on the two magnetic pole faces.

The bobbin 44 is substantially rectangular.
Regarding the mounting of the magnet and bobbin, the conduit as shown in FIG. 3 reciprocates in the vertical direction. Thus, the upper and lower horizontal windings of coil 45 intersect the magnetic flux field of substantially uniform magnet 42 at right angles. This induces a potential corresponding to a linear function of the relative velocity of the coil 45 with respect to the adjacent magnet 42. The pole faces 47 and 48 of magnet 42 are preferably sufficiently separated so that the magnetic flux there is perpendicular to each face. The outer shape of the magnet 42 is such that its pole faces 47, 48 are larger than the maximum amplitude of the conduit, which ensures that the upper and lower parts of the coil 45 are kept in a uniform magnetic field.

Preferably, the pole faces 47, 48 are coil 45 during the vibration of the conduit and the deflection induced by the Coriolis force.
Positioned such that the gap between and does not change. Of course, if desired, magnet 42 may be attached to the conduit and bobbin 44 may be fixedly attached to the coil instead of the arrangement described above.

Returning to FIG. 5, the sensor circuits are arranged in parallel--one with a dash--and the set of coils 45, 45 'already described for speed sensor 40 is depicted. In the measuring device according to the invention, the output signals from such coils 45, 45 'are combined on the basis of the Coriolis force induced in response to the mass flow and the vibrations of the conduits respectively produced by a drive mechanism such as 25 in FIG. In fact, it has a waveform in which the frequency component and the component due to the fluctuation of the frequency caused by the disturbance such as shock, fluctuation of temperature, fluctuation of fluid pressure, etc.

According to the measuring device of the invention, the outputs of the speed sensors 45, 45 'are fed to the accumulating junctions 48, 48' and from there to further integrators 49, 49 '. It will be appreciated that several stages of integrators may be provided to reduce sensitivity to disturbances. The outputs of the integrators 49, 49 'are connected to reduction filters 50, 50' for passing the low frequency signal components from the speed sensor coils 45, 45 ', respectively.
Further, each is negatively fed back to the accumulation junction. Filter 50,
Reference numeral 50 'includes resistors 51 and 51'; capacitors 52 and 52 'and amplifiers 53 and 53', and has a conventionally known arrangement as shown. Thus, the speed sensors 45, 4
In processing the signal from 5 ', the low frequency components actually cancel each other out, so that they are substantially removed from the output of the integrator 49, 49'. The outputs of the integrators 49, 49 'are sent via resistors 54, 54' to amplifiers 55, 55 'operating at saturation level. As is well known, amplifiers 55 and 55 'convert an oscillating waveform input into an output of a clipped signal waveform having an approximately truncated sawtooth waveform.

Each of the comparators 60 and 60 'is connected at its one input terminal to the output from the amplifier 55 or 55' through a resistor 57 or 57 '. The reference inputs of the comparators 60, 60 'are connected to the reference voltage via resistors 63, 63', respectively, and also resistors 65, 66 having different resistance values, for example.
Grounded through. Therefore, the reference voltage Va is calculated by the comparator 6
0 and Vb are provided to the comparator 60 '. On the other hand, the square wave output of the comparator 60 is biased to the "ON" position as a function of the voltage Va. That is, the amplifier 55
At the position of the bias line drawn in relation to the output of
FF ″. Comparator 6 by the same means
The output signal from 0'is biased to the "OFF" position. That is, it is switched again at the position of the bias line b as a function of the reference voltage Vb. This bias is applied to the sensor 4 over the dynamic range of the flow meter 10.
Even if 5 fluctuates, that is, the flow rate in the conduit becomes maximum, the comparator 6 is preceded by the rising waveform from the comparator 60 '.
It is adjusted to give a rising waveform from zero.

The rectangular wave outputs of the comparators 60 and 60 'are supplied to the reading circuit 70. This reading circuit is described, for example, in U.S. Pat. No. 4,187,721 or in the publication "Instruction Manual Model B Mass Flow Mete
r) ”, Micro Motion, 7070 Winchester C
ircle, Boulder, Colorado 80301, which is the same as that which calculates the time difference, calculates the mass flow rate in a desired mass unit per unit time, and displays the value.

As will be described below, the read circuit 70 is basically described in detail in an up-down counter or "Model B Mass Flowmeter Instruction Manual", the details of which are described, for example, in US Pat. No. 4,187,721. The analog integrator that is being constructed. Any of these suitable circuits are intended to measure the delay time between the rising and falling portions of the rectangular wave output of the comparator 60, 60 'input to the reading circuit. .

As is apparent from FIGS. 1 to 5 and the above description, several important advantages are guaranteed by the measuring device according to the invention using the sensor and the circuit described above. An improved means of measuring the Coriolis force that causes the elastic deflection of the conduit is provided by producing an analog signal that represents an accurate linear function of the overall oscillatory motion of the conduit. Specifically, the sensors 33, 33 'of FIG. 1 produce a signal which is a linear function of the overall actual oscillatory motion of the conduit.

In general, a multistage installation is preferable, but instability is observed in the circuit when an extremely large number of integration stages are provided. Those skilled in the art should easily be aware of the number of stages in which the advantage of providing the integrator in the actual flow meter system is impaired.

The speed sensor 40 as shown in FIGS. 3 and 4 is economical and appears to be the most effective sensor 33, 33 '. Although this is contrary to the theoretical advantage, it is largely due to the ease of assembly, availability of appropriate circuit elements, and stability.

When the velocity sensor 40 is adopted in the Coriolis force type mass flowmeter 10 as shown in FIG. 1 and the sensor output is integrated over one stage or multiple stages, the most troublesome use condition in the past, for example, in a conduit. Long-term stability can be obtained even under conditions in which the temperature of the fluid flowing through the material fluctuates substantially by 200 ° C. or more.

Even if the refrigerating agent falls directly onto the conduit, the sensitivity and accuracy of the Coriolis force type mass flowmeter 10 cannot be destroyed in the present invention for several cycles or more. In the case of a vibrating tube type Coriolis force flowmeter using conventional sensing, signal processing and measuring techniques in the prior art, such conditions would result in significant operational disruption.

The operation of the flow meter will be more easily understood by referring to the charts showing the signals and timings shown in FIGS. 6 to 9. For discussion of these figures and operation of read circuit 70, circuit 70 of FIG. 5 is basically preferably an add-subtract counter such as that described in U.S. Pat. No. 4,187,721, or a "Model B mass flow rate". It is easy to understand if it is one of the integrators described in "Measurement instruction manual". Since either an add-subtract counter or an analog integrator circuit accomplishes the same purpose, the following discussion of how read circuit 70 operates will not be repeated for each case for convenience. Instead, the compound word "counter / integrator", which means that it has either function, is used. The outputs of the integrators 49, 49 'of FIG. 5 are, as shown in FIG. 6, free of flow in the conduit after the frequency components other than the vibration due to the Coriolis force have been eliminated as described above. Under the condition, they have the same repeating waveform. Reference voltage Va to each comparator 60, 60 '
And Vb are different, the square wave input from the comparators 60, 60 'to the reading circuit 70 is as shown in FIG.
The one from comparator 60 is at the "ON" level for a longer time than the one from comparator 60 '. Therefore, the subtraction count / integration initiated by the rising edge of the signal from the comparator 60 is terminated by the signal from the comparator 60 'and is always maintained at a positive value along with the count / integration signal reher which represents the delay time between these events. Be drunk

Similarly, the addition counting / integrating unit of the reading circuit 70 starts its operation at the falling edge of the signal from the comparator 60 'and ends its operation at the falling edge of the signal from the comparator 60'. Therefore, it is also maintained at a positive value representing the delay time. As mentioned above, this relationship is maintained by adjusting the relative magnitudes of the reference voltages Va, Vb. Under no flow conditions, counting / integrating is the same for addition and subtraction.

With reference to FIG. 8, it will be appreciated that the repetitive signals output from integrators 49, 49 'will undergo a shift under conditions of flow in the conduit.

The relative length of time that the signal from the comparator 60 is "ON" also depends on the signal from the comparator 60 'being "N".
Although the relative length of the time "O" does not change, the delay time between the signal changes of both changes as shown in FIG.

The period in which the subtraction count / integration is recorded in the reading circuit 70 does not coincide with the period in which the addition count / integration is also recorded. The difference between the two represents the mass flow rate. Briefly, the subtraction count / integration and the addition count / integration performed by the read circuit 70 under no flow conditions as shown in FIG. 6 are identical because the conduit is undeflected about the axis O--O. Yes,
The reading circuit 70, which adds the subtraction count / integration and the addition count / integration together, indicates no flow. On the other hand, in the presence of flow, as shown in FIG. 9, the rising stroke of the oscillating conduit causes the square wave signal from the comparator 60 to move forward relatively, while the square wave signal from the comparator 60 '. Is protracted. As a result, the reading circuit 70
Increment count / integral input to
Integral input is reduced.

Therefore, the mass flow rate through the oscillating mass flow meter is a function of the difference between the add count / integral and the subtract count / integral, as shown in FIG.

In summary, the present invention addresses the problem of structural and frequency variations in the oscillatory behavior of a conduit due to variations in external physical factors affecting the vibration of the conduit. A sensor that produces an analog signal as a linear function of the overall oscillatory motion of the conduit is used to integrate and filter the frequency components corresponding to physical changes other than the vibration caused by the vibration drive mechanism throughout the vibration. By using a circuit for erasing and erasing, a stable and accurate mass flow measuring device according to the present invention is provided. The output of the sensor is
It is preferable that the integration is performed in one step at least once,
Particularly in the case of the output signal from the acceleration sensor, it is desirable to integrate several stages. When the signals are generated in this way, i.e., a signal linearly related to the overall vibration of the conduit is obtained, these signals are easily converted into, for example, a square wave,
The delay time between these signals is monitored as corresponding to the deflection of the opposite part of the tube by the Coriolis force and the mass flow rate through the flow meter is accurately measured.

The invention described above and by way of illustration is
Although the present invention relates to the embodiment using a suitable example of the flow meter and the sensor, this can be variously modified.

[Brief description of drawings]

FIG. 1 is a schematic view of a mass flow rate measuring device of the present invention.

FIG. 2 illustrates the motion of a typical vibrating conduit used in the present invention.

FIG. 3 shows a preferred example of the magnet-coil sensor structure of the flow meter shown in FIG. 1 and is depicted in one arrangement with respect to an oscillating conduit. Those skilled in the art will understand that this arrangement is one example among many.

FIG. 4 depicts the same preferred magnet-coil velocity sensor detail arrangement as in FIG. 3 and illustrates one preferred dimensional relationship between the coil and pole faces. It will be understood by those skilled in the art that the coil perimeter is placed in a uniform magnetic flux field, independent of both the oscillating motion of the conduit and the long-term distortion of the spatial orientation of the conduit due to fluctuations in external conditions. Ah

FIG. 5 is an electronic circuit that can be used with the sensor shown in FIGS.

FIG. 6 is a diagram illustrating a state after a signal substantially the same as the signal shown in FIG. 2 is compensated for an external error signal, assuming ideal signal generation in the case of no flow rate.

FIG. 7 illustrates a preferred mass flow meter read signal corresponding to the sensor output of FIG.

FIG. 8 is a view similar to FIG. 6 when there is a flow rate after compensating for an external error signal as it occurs.

FIG. 9 illustrates a preferred mass flow meter read signal corresponding to the sensor output shown in FIG.

[Explanation of symbols]

10: Flowmeter, 12: Mounting platform, 14:
Conduit, 15: inflow port, 16: outflow port, 18, 20: side leg part, 33, 33 ': sensor, 45, 45': coil,
42: Magnet.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-54-52570 (JP, A) JP-A-51-126194 (JP, A) JP-B-43-26009 (JP, B1) JP-B-52- 34481 (JP, B1) Jitsuko Sho 54-15044 (JP, Y1)

Claims (1)

[Claims] (A) at least one continuous conduit having both open ends fixed and adapted to be oscillated by being biased by a driving means; and (b) both ends fixed and substantially to said conduit. A vibrating member disposed in parallel with the vibrating member, the vibrating member having substantially the same resonance frequency as that of the conduit and operating in a tuning fork shape by vibrating in an opposite phase to the conduit, c) a drive means for vibrating the conduit and the vibrating member, and (d) a sensor means comprising at least a pair of substantially identical sensors for generating an electrical signal in response to movement of the conduit, the pair of sensor means comprising: Along the conduit each of the sensors at (i) a position substantially equidistant from each end of the conduit and (ii) a position substantially equidistant from a central point of the conduit. The sensor hand that is arranged , (E) signal processing means, (f) the mass flow rate of the fluid flowing through the conduit, the conduit portion adjacent to one of the pair of sensors passing through a given point of its vibration path. To indicate as a function of the time difference between each of the time points and all the time points at which the portion of the conduit adjacent the other sensor of the pair of sensors passes the point corresponding to the given point in its vibration path. Mass flow rate reading means, wherein the sensor means comprises at least a pair of magnetic speed sensors, each magnetic speed sensor is composed of a magnet and a coil, and the coil always corresponds to the coil. The magnet and the coil are arranged so as to move in a uniform magnetic field of the magnet. Together to generate a continuous signal representative of the speed of said conduit portion adjacent to the sensor through the body, said signal processing means includes at least a pair of circuit portion formed in the same circuit elements,
Each of them comprises a circuit portion similarly connected to the output of the coil of one of the pair of magnetic velocity sensors, and each circuit portion includes at least one stage integrator of the output from the sensor coil. A Coriolis mass flow measuring device for measuring the mass flow rate of a fluid, characterized in that